Japan’s Coast Guard says at least two Chinese government vessels have entered territorial waters near Japanese-controlled islands, as a dispute escalates on the sensitive anniversary of Japan’s invasion of China.

The vessels are among 11 Chinese ships spotted Tuesday near the East China Sea islands, known as Senkaku in Japan and Diaoyu in China. Japanese authorities earlier turned away another Chinese patrol ship.

Two Japanese activists briefly landed on one the islands Tuesday, prompting an angry response from China’s Foreign Ministry, which called the act a “gravely provocative” violation of Chinese sovereignty.

The dispute over the mostly uninhabited islands led to a day of anti-Japan protests in major cities across China. In Beijing, at least 1,000 protesters marched outside the Japanese embassy, holding signs, chanting nationalistic slogans and calling for China to defend its claim to the islands. Many Japanese companies, including Honda, Toyota, Mitsubishi and Panasonic have cut back operations in China because of sporadic outbreaks of violence.